The studies conducted in the past year have demonstrated that: Ro-07-0582 radiosensitizes not only tumors but also the kidney and the spinal cord; that addition of WR-2721 after Ro-07-0582 but before X-ray exposure can reverse this radiosensitization; that when both Ro-07-0582 (6mM) and a free sulfhydryl, cysteine (8mM), are present during exposure to radiation in vitro, sensitization predominates if the cells are hypoxic, while protection predominates if the cells are well-oxygenated; that WR-2721 can protect the kidney against cis-platinum without altering its anti-tumor effectiveness and can protect the bone marrow against cyclophosphamide and HN2 without altering their anti-tumor effectiveness; and that the toxicity of Ro-07-0582 is associated with the reduction of the nitro-group and this reduction can be accomplished by xanthine oxidase in simple chemical systems.